LIFE AT AND NEAR SURFACE 135 



growths of the north, so the marine growth 

 of the warm, equatorial seas is more luxuriant, 

 more varied and ranker than submarine 

 growth in northern seas. This only applies 

 to the shallower waters, however, for at great 

 depths the water is always cold and many of 

 the same animals occur in both tropical and 

 northern seas. 



We naturally always associate corals with 

 the tropical seas, for the greater number of 

 corals are natives of warm waters and, more- 

 over, the majority of tropical corals can live 

 only within a hundred feet or so of the sur- 

 face; but even in the far north corals occur 

 abundantly in deep water. Some are found 

 as far north as Greenland, and one species, 

 which is common in northern seas, is found at 

 low-water mark on the New England coast. 

 So, too, sponges, which we always associate 

 with the tropics, are not confined to tropical 

 seas but great numbers occur in the waters of 

 the polar regions and in all seas between the 

 tropics and the arctic and antarctic circles. 

 Many of the more noteworthy and largest 

 forms of these northern sponges are found 



